How can I create a multiboot USB stick from Linux?

You can refer to https://www.pendrivelinux.com/multiboot-create-a-multiboot-usb-from-linux/

It works for me!

Above you can see that I am able to boot Ubuntu 16.03 as well as 18.04 with one USB stick w/o problem.

But somehow you've to disable security boot in BIOS.

Enjoy~

How can I setup a proxy server in Ubuntu 16.04?

Step1. Install package squid

# sudo apt-get install -y squid

Step2. To setup common proxy settings:

# sudo vi /etc/squid/squid.conf

To add some lines below:

# line 977

acl lan src 192.168.1.0/24

(where 192.168.1.0 means network you would like to allow client to access your proxy server)

# line 1189

http_access allow lan

(Allow lan here)

# line 1602

http_port 3128

(To modify default proxy port if needed)

Step3. Restart squid

# sudo systemctl restart squid

Step4. Examine squid service

# sudo systemctl status squid

● squid.service - LSB: Squid HTTP Proxy version 3.x

Loaded: loaded (/etc/init.d/squid; bad; vendor preset: enabled)

Active: active (running) since 四 2018-04-26 15:24:04 CST; 1min 56s ago

Docs: man:systemd-sysv-generator(8)

Process: 3088 ExecStop=/etc/init.d/squid stop (code=exited, status=0/SUCCESS)

Process: 3119 ExecStart=/etc/init.d/squid start (code=exited, status=0/SUCCESS)

CGroup: /system.slice/squid.service

├─3159 /usr/sbin/squid -YC -f /etc/squid/squid.conf

├─3161 (squid-1) -YC -f /etc/squid/squid.conf

├─3162 (logfile-daemon) /var/log/squid/access.log

└─3163 (pinger)

四 26 15:24:04 uc16-VirtualBox systemd[1]: Starting LSB: Squid HTTP Proxy version 3.x...

四 26 15:24:04 uc16-VirtualBox squid[3119]: * Starting Squid HTTP Proxy squid

四 26 15:24:04 uc16-VirtualBox squid[3159]: Squid Parent: will start 1 kids

四 26 15:24:04 uc16-VirtualBox squid[3119]: ...done.

四 26 15:24:04 uc16-VirtualBox systemd[1]: Started LSB: Squid HTTP Proxy version 3.x.

四 26 15:24:04 uc16-VirtualBox squid[3159]: Squid Parent: (squid-1) process 3161 started

# netstat -tupln | grep 3128

tcp6 0 0 :::3128 :::* LISTEN 3161/(squid-1)

Done ~

In proxy client side:

You can use tcpdump or wireshark to ensure that http request will go to proxy server after you configured http proxy server within browser.

root@server1:~$ sudo tcpdump -n -v -i any port 3128

tcpdump: listening on any, link-type LINUX_SLL (Linux cooked), capture size 262144 bytes

15:29:06.382845 IP (tos 0x0, ttl 64, id 2257, offset 0, flags [DF], proto TCP (6), length 145)

192.168.1.211.40994 > 192.168.1.254.3128: Flags [P.], cksum 0x85a5 (incorrect -> 0x9ba8), seq 670754847:670754940, ack 314235908, win 237, options [nop,nop,TS val 1731217504 ecr 1884649606], length 93

15:29:06.383195 IP (tos 0x0, ttl 64, id 35299, offset 0, flags [DF], proto TCP (6), length 212)

192.168.1.254.3128 > 192.168.1.211.40998: Flags [P.], cksum 0xbf6c (correct), seq 2355697405:2355697565, ack 1986317666, win 486, options [nop,nop,TS val 1884649610 ecr 1731217476], length 160

15:29:06.383264 IP (tos 0x0, ttl 64, id 17423, offset 0, flags [DF], proto TCP (6), length 52)

192.168.1.254.3128 > 192.168.1.211.40994: Flags [.], cksum 0xaba6 (correct), ack 93, win 503, options [nop,nop,TS val 1884649610 ecr 1731217501], length 0

15:29:06.383359 IP (tos 0x0, ttl 64, id 2258, offset 0, flags [DF], proto TCP (6), length 1353)

192.168.1.211.40994 > 192.168.1.254.3128: Flags [P.], cksum 0x8a5d (incorrect -> 0x8fe0), seq 93:1394, ack 1, win 237, options [nop,nop,TS val 1731217505 ecr 1884649610], length 1301

15:29:06.384198 IP (tos 0x0, ttl 64, id 9911, offset 0, flags [DF], proto TCP (6), length 268)

How can I setup a Linux NAT Router in Ubuntu?

Steps:

1. Enable packet forwarding for IPv4 between NICs:

• Open and edit /etc/sysctl.conf
• Ucomment net.ipv4.ip_forward=1
• To execute command sysctl -p

2. Create a postrouting rule within iptables:

• iptables -t nat -A POSTROUTING -o enp0s8 -s 192.168.1.0/24 -j MASQUERADE
• Where enp0s8 is WAN and 192.168.1.0/24 is LAN, please modify those parameters depend on your environment.

3. Save and restore iptables rule after reboot:

• Save rules: iptables-save > /etc/iptables.save
• Restore rules:
• Open and edit /etc/network/interfaces to add pre-up.....

# interfaces(5) file used by ifup(8) and ifdown(8)
auto lo
iface lo inet loopback
auto enp0s3
iface enp0s3 inet static
address 192.168.1.254
netmask 255.255.255.0
pre-up iptables-restore < /etc/iptables.save

Done~

如何在Ubuntu 16.04 desktop 透過PXE安裝Ubuntu?

在開始之前，請先準備與安裝相關的service在Ubuntu desktop 16.04 LTS:

準備：
1. Download Ubuntu desktop ISO
2. Download PXE bootloader

安裝：
1. DHCP Server

$ sudo apt-get install isc-dhcp-server

2. TFTP Server

$ sudo apt-get install tftpd-hpa inetutils-inetd

3. NFS Server

$ sudo apt-get install nfs-kernel-server

配置：
1. DHCP Server:

$ sudo vi /etc/dhcp/dhcpd.conf

 subnet 192.168.1.0 netmask 255.255.255.0 {
 range 192.168.1.200 192.168.1.253;
 option domain-name-servers 8.8.8.8;
 option routers 192.168.1.1;
 option broadcast-address 192.168.1.255;
 default-lease-time 600;
 max-lease-time 7200;
 next-server 192.168.1.254;
 filename "pxelinux.0";
 }

 $ sudo systemctl restart isc-dhcp-server

 2. TFTP Server:

$ sudo vi /etc/default/tftpd-hpa

TFTP_USERNAME="tftp"
TFTP_DIRECTORY="/var/lib/tftpboot"TFTP_ADDRESS=":69"
TFTP_OPTIONS="--secure"
RUN_DAEMON="yes"
OPTIONS="-l -s /var/lib/tftpboot"

$ sudo vi /etc/xinetd.conf

tftp    dgram   udp    wait    root    /usr/sbin/in.tftpd /usr/sbin/in.tftpd -s /var/lib/tftpboot

$ sudo systemctl restart tftpd-hpa 

3. PXE bootloader:

$ tar -xJf syslinux-6.03.tar.xz
$ cd syslinux-6.03
$ sudo cp bios/core/pxelinux.0 /var/lib/tftpboot
$ sudo cp bios/com32/lib/libcom32.c32 /var/lib/tftpboot
$ sudo cp bios/com32/libutil/libutil.c32 /var/lib/tftpboot
$ sudo cp bios/com32/elflink/ldlinux/ldlinux.c32 /var/lib/tftpboot
$ sudo cp bios/com32/menu/vesamenu.c32 /var/lib/tftpboot
$ mkdir /var/lib/tftpboot/pxelinux.cfg
$ sudo vi /var/lib/tftpboot/
pxelinux.cfg/default 

DEFAULT vesamenu.c32
MENU TITLE Network boot
LABEL ubuntu-mate-16.04.2-desktop-amd64
  MENU LABEL ubuntu-mate-16.04.2-desktop-amd64
  KERNEL vmlinuz.efi
  APPEND initrd=initrd.lz root=/dev/nfs boot=casper netboot=nfs nfsroot=192.168.1.254:/var/nfs/ubuntu_desktop splash -- 

* Remember to copy vmlinuz.efi and initrd.lz to the folder /var/lib/tftpboot from Ubuntu ISO.
* 補充: 針對18.04要修改一下設定檔如下:
  APPEND initrd=./u18/initrd_ubuntu18.04.lz root=/dev/nfs boot=casper netboot=nfs nfsroot=192.168.1.254:/var/nfs/ubuntu18.04 splash toram --

4. NFS file Server:

$ sudo mount -o loop ubuntu-16.04.3-desktop-amd64.iso /mnt/
$ sudo mkdir -p /var/nfs/ubuntu_desktop
$ sudo cp -rf /mnt/* /var/nfs/ubuntu_desktop/
$ sudo vi /etc/exports
/var/nfs/ubuntu_desktop *(ro,sync)

$ sudo systemctl restart nfs-kernel-server

$ showmount -e localhost 

Export list for localhost:
/var/nfs/ubuntu_desktop *

Boot from Network boot:

Done!

How can I move Launcher from left to the buttom on Ubuntu 16.04?

It's very simple, and it works for me even if I reboot or re-login the system b/c Ubuntu will remember it.

Steps:
1. Open a terminal

2. To execute "gsettings set com.canonical.Unity.Launcher launcher-position Bottom"

Done~

How can I get detail information of USB device?

The command lsusb, which able to list all USB devices of machine below:

lawrence@Lawrence-ThinkPad-X200:~$ lsusb
Bus 002 Device 004: ID 7392:7711 Edimax Technology Co., Ltd EW-7711UTn nLite Wireless Adapter [Ralink RT2870]
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 008 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 007 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 006 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 001 Device 003: ID 17ef:480c Lenovo Integrated Webcam
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 005 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 004 Device 002: ID 08ff:2810 AuthenTec, Inc. AES2810
Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub

However, I would like to know more informations. For example, speed, vendor, manufacturer......, etc. And there is a command usb-devices, which can help me.

lawrence@Lawrence-ThinkPad-X200:~$ usb-devices 

T:  Bus=02 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#=  4 Spd=480 MxCh= 0
D:  Ver= 2.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS=64 #Cfgs=  1
P:  Vendor=7392 ProdID=7711 Rev=01.01
S:  Manufacturer=RalinkS:  Product=802.11 n WLAN
S:  SerialNumber=1.0
C:  #Ifs= 1 Cfg#= 1 Atr=80 MxPwr=450mA
I:  If#= 0 Alt= 0 #EPs= 7 Cls=ff(vend.) Sub=ff Prot=ff Driver=rt2800usb

T:  Bus=04 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#=  1 Spd=5000 MxCh= 2
D:  Ver= 3.00 Cls=09(hub  ) Sub=00 Prot=03 MxPS= 9 #Cfgs=  1
P:  Vendor=1d6b ProdID=0003 Rev=04.13
S:  Manufacturer=Linux 4.13.0-32-generic xhci-hcd
S:  Product=xHCI Host Controller
S:  SerialNumber=0000:0d:00.0
C:  #Ifs= 1 Cfg#= 1 Atr=e0 MxPwr=0mA
I:  If#= 0 Alt= 0 #EPs= 1 Cls=09(hub  ) Sub=00 Prot=00 Driver=hub

Above you can see the Spd=480/USB 2.0, and Spd=5000/USB 3.0.

[Shell script] Find user in system

The first way:

#!/bin/bash

if [ $# -eq 0 ]
then
 echo "Usage: $0 lawrence"
else
  grep "\<$1\>" /etc/passwd > /dev/null
  RETVAL=$?
  if [ $RETVAL -eq 0 ]
  then
   echo "Username $1 was found in the system"
  else
   echo "Cannot find username $1"
 fi
fi

The second way:

[ $# -eq 0 ] &&  { echo "Usage: $0 lawrence" ; exit 1; }

grep "\<$1\>" /etc/passwd > /dev/null
RETVAL=$?

[ $RETVAL -eq 0 ] && echo "Username $1 was found in the system" || echo "Cannot find username $1"

How can I add EPEL reop on CentOS 7.x?

It's quite simple, just two commands below:

# yum install epel-release

# yum repolist

Sample output:

How can I disable dnsmasq listen port 53 on the Ubuntu 16.04 LTS?

By default the DNS Server of Ubuntu 16.04 LTS will be 127.0.0.1:53, i.e., localhost.




Therefore, system will forward DNS query to the localhost first, and forward to the DNS server which obtained from the DHCP server afterward.

Actually, I didn't prefer this method, so that I would like to turn off  this mechanism via steps were listed below:

Steps:
1. Open /etc/NetworkManager/NetworkManager.conf

2. To disable dnsmasq


3. Restart NetworkManager


4. Examine /etc/resolv.conf


Done.

How can I switch multi-user or graphical mode via one command? (Systemd)

To switch multi-user to graphical mode (runlevel 3 to runlevel 5)

# systemctl set-default graphical && reboot




To switch graphical to multi-user mode (runlevel 5 to runlevel 3)

# systemctl set-default multi-user && reboot

How to know the system and service manage daemon of your Linux? (SysVinit or Systemd)

It's simple, just check your pid 1. (ps --pid 1)

SysVinit:


Systemd:

How can I backup and restore MBR via dd command?

Check device name of HD:
# lsblk

Backup MBR:
# dd if=/dev/sda of=file bs=1 count=512

Note:
1. The size of MBR is 512 bytes and located in the first sector.
2. Of cause you need to save MBR backup file somewhere else.

Restore MBR:
# dd if=file of=/dev/sda bs=1 count=512

Snap commands

Here I want to list some of snap commands that I often use.

Also here is a website to understand all of snap commands:
https://snapcraft.io/docs/reference/snap-command


Log on to a snap store:

lawchiu@localhost:~$ sudo snap login xxx.xxx@gmail.comPassword of "xxx.xxx@gmail.com":
Login successful

Log out snap store:

lawchiu@localhost:~$ snap logout

Update snap:

lawchiu@localhost:~$ snap refresh
All snaps up to date

List installed snap:
lawchiu@localhost:~$ snap list
Name             Version       Rev   Developer            Notes
checkbox-snappy  2.2           859   ce-certification-qa  devmode
core             16-2.27.5     2774  canonical            core
hello            2.10          20    canonical            -
pc               16.04-0.8     9     canonical            gadget
pc-kernel        4.4.0-83.106  68    canonical            kernel
lawchiu@localhost:~$

Remove snap:
lawchiu@localhost:~$ snap remove hello
hello removed

Find packages:
lawchiu@localhost:~$ snap find 

Install and use glances on Ubuntu

Glances is a great tools which able to monitor CPU, Memory, Disk, Network statistics... etc.

Please refer to glances website for details.

Steps:
1. Install glances via apt:
lawrencechiu@lawrencechiu-HP-Compaq-6005-Pro-SFF-PC:~$ sudo apt-get install glances


2. Executed glances:
lawrencechiu@lawrencechiu-HP-Compaq-6005-Pro-SFF-PC:~$ sudo glances

3. Then you can see CPU usage, Memory status, SWAP, Network statistics, Disk IO, Disk usage, and PID info in one screen below:

Green means OK
Blue means CAREFUL
Purple means WARNING
Red means: CRITICAL

Hotkey:

 a  Sort processes automatically          b  Bytes or bits for network I/O
 c  Sort processes by CPU%                l  Show/hide alert logs
 m  Sort processes by MEM%            w  Delete warning alerts
 p  Sort processes by name                  x  Delete warning and critical alerts
 i  Sort processes by I/O rate               1  Global CPU or per-CPU stats
 t  Sort processes by CPU times          h  Show/hide this help screen
 d  Show/hide disk I/O stats                T  View network I/O as combination
 f  Show/hide filesystem stats             u  View cumulative network I/O
 n  Show/hide network stats                F  Show filesystem free space
 s  Show/hide sensors stats                  g  Generate graphs for current history
 2  Show/hide left sidebar                    r  Reset history
 z  Enable/disable processes stats        q  Quit (Esc and Ctrl-C also work)
 e  Enable/disable top extended stats
 /  Enable/disable short processes name
 D  Enable/disable Docker stats

Enjoy~

How can I remote ssh login to the Ubuntu 16.04 LTS via root?

By default you are unable to ssh login to the Ubuntu 16.04 LTS via root, but you can enable it step by step as following:

1. Login to the system via regular user account.

2. Set password to root account (Due to root password is empty by default)

sudo passwd root

3. To modify the configuration file of sshd_config (Marked PermitRootLogin prohibit-password, and added PermitRootLogin yes )

sudo vi /etc/ssh/sshd_config

# Authentication:

LoginGraceTime 120

#PermitRootLogin prohibit-password 

PermitRootLogin yes 

StrictModes yes

4. Restart sshd

 sudo systemctl restart ssh

Done.

Unable to logon to the Ubuntu Core with 2nd SSH public key?

After I added a new SSH public key into my Ubuntu One. However, I am unable to logon to the Ubuntu Core system with this new key, therefore I logon to the Ubuntu Core by original public key.

Afterward, I noticed that my system didn't sync up a new public key from Ubuntu One automatically.

Until now I have no idea if this is a defect or limitation, please advice, if any.

Workaround:

Added 2nd public key via manually into the ~/.ssh/authorized_keys

How to deploy Ubuntu Core from KVM to VirtualBox?

Steps:
1. Download Ubuntu Core of KVM image from URL below:
https://developer.ubuntu.com/core/get-started/kvm

2. To decompress xz.

3. To convert the format of img to the vdi via VBoxManage command below:

VBoxManage.exe convertdd ubuntu-core-16-amd64.img ubuntu-core-16-amd64.vdi

4. Import vdi file above to the VirtualBox without issue.

Python的額外錯誤處理

Example:

try:

    data=open('open_file.txt')

    for each_line in data:

        try:

            (var1,var2)=each_line.split(":",1)

            print(var1)

            print(var2)

        except:

            print(each_line)

    data.close()

except:

    print('File is not existing') 

透過Python的try & except，程式碼果真變得很簡潔～

如何將Python程式模組化？

今天學習了如何將Python function模組化.

實際的步驟:

1. 撰寫python, 存檔為*.py
2. 撰寫setup.py for metadata (*.py跟setup.py需在同一個目錄下)
3. 執行python setup.py sdist 以建構發行套件檔案4. 執行python setup.py install 來安裝發行套件到本地端

開啟一個新檔案把module 用import的方式匯入, 透過引用正確的module名稱跟函式就可以執行了.

Cockpit

I saw this tools recently, and I am definitely to try it. :)

Cockpit